Referring to FIG. 3, there is illustrated a configuration of a conventional dishwasher.
As shown in FIG. 3, dishwasher main body 1 has washer tub 2 therein, and water or warm water is supplied into washer tub 2 by water supply valve 3. Here, the supply of wash water is automatically stopped by shutting water supply valve 3 once the water in washer tub 2 reaches an appropriate preset water level which is detected by a water level detector (not shown). Water drainage outlet 4 is disposed on the bottom portion of washer tub 2, and communicates with washing pump 5 driven by a motor for use in circulating wash water in washer tub 2. Further, strainer 6 for filtering particulate food debris from the wash water is installed in water drainage outlet 4.
The operation of a dishwasher in accordance with the above configuration will now be described. Wash water supplied in washer tub 2 is suctioned by washing pump 5 through strainer 6 and is then injected into wash nozzle 7 disposed in the lower portion of washer tub 2 from washing pump 5. Once wash water has been sprayed by wash nozzle 7 onto soiled items 8 to be cleaned (kitchen and dining ware), it is circulated back to water drainage outlet 4 through a water passageway. At this point, solid food particulates removed from items 8 to be cleaned are introduced into strainer 6 in wash water, and any debris too large to pass through strainer 6 are collected in strainer 6.
Further, heater 9 for heating wash water is disposed between wash nozzle 7 and the bottom portion of washer tub 2. Disposed above wash nozzle 7 is rack 10 for arranging items 8 to be cleaned therein in an orderly manner so they can be subjected to more effective spraying of wash water resulting in more efficient cleaning. Moreover, water drain pump 11 is for use in discharging wash water from the dishwasher. Controller 12 controls electrical components such as water supply valve 3 and washing pump 5 (see, for example, Japanese Patent Laid-Open Application No. 2003-210378).
However, the conventional dishwasher having the above configuration is not capable of removing all types of food debris. Particularly, heavy or stubborn debris which are dried-on or baked-on material remaining on kitchen ware items after preparing certain foods (e.g., gratin or savory streamed egg custard) cannot be removed by the conventional dishwasher.
To solve this problem, it has been proposed to add a pre-washing step to allow more concentrated detergent solution to coat and remain on kitchen and dining items for a period of time. Adding this step improved the cleaning ability of the conventional dishwasher model, thereby enabling it to remove stubborn or heavy debris it could not before.
In this case, when using a mist generator having an ultrasonic vibrator to promote coating of high concentration detergent solution on kitchen or dining ware items to be cleaned, food debris in wash water or mineral dissolved in water with high hardness, (e.g., ground or well water), may deposit and harden thereafter on the vibrating surface of the ultrasonic vibrator. Consequently, such deposits affect the operation of the ultrasonic vibrator by deteriorating its power considerably or causing it to malfunction.